DAX-8 Resin Research Articles

Fouling characteristics in a membrane bioreactor coupled with anaerobic–anoxic–oxic process for coke wastewater treatment

Experiments were conducted to investigate the fouling characteristics of a membrane bioreactor combined with anaerobic–anoxic–oxic process for coke wastewater treatment. Supernatant from the oxic tank was characterized as different hydrophilic/hydrophobic fractions by DAX-8 resin, with joint size partition also undertaken. Polysaccharides and proteins, mainly the fraction with molecular weight above 100 kDa, were liable to accumulate in the supernatant. Hydrophilic fraction, mainly contributing to the subclass of molecular weight above 100 kDa, was found most likely responsible for the flux deterioration by means of dead-end filtration tests. Analyses of particle and membrane pore size distribution revealed that major foulants had size comparable to the pore diameter. It can be inferred that steric factor (i.e. size exclusion) behaved primarily in the initial stage of fouling, while the role of hydrophobic interaction was of less significance.

A systematic insight into fouling propensity of soluble microbial products in membrane bioreactors based on hydrophobic interaction and size exclusion

Soluble microbial products (SMPs) contained in membrane bioreactor (MBR) supernatant have been proved to be main foulants. To obtain a comprehensive understanding of the fouling potential of SMPs on the basis of both hydrophilic/hydrophobic properties and molecular size, MBR supernatant of a pilot-scaled system treating municipal wastewater was partitioned into different hydrophilic/hydrophobic fractions by DAX-8 resins, with joint size partition of hydrophilic fraction also undertaken. A series of stirred dead-end filtration tests were conducted to investigate the flux decline. Hydrophilic fraction was found the dominant foulant responsible for flux deterioration, which was mainly attributed to the subclass of molecular weight above 100 kDa. The molecular weight distribution and atomic force microscopy images indicated that large molecules in hydrophilic fraction plugged the membrane pores. The backwash tests showed the flux decline caused by hydrophilic fraction was much less recoverable by hydraulic cleaning. It can be inferred that steric factor, i.e. size exclusion was the primary cause in the initial stage of fouling, while the role of hydrophobic interaction was of less significance. Additional modeling work indicates that the main fouling mechanism was complete blocking, further confirming the predominance of size exclusion contributing to membrane fouling by SMPs in MBR supernatant.

Application of a refractory organic matter quantification method to wastewater effluents

An already established analytical method for the quantification of freshwater refractory organic matter (often called humic substances) has been applied to organic matter from a wastewater treatment plant's effluent and a number of downstream locations impacted by the treatment plant. The method is based on measuring the peak currents obtained by adsorptive stripping voltammetry of the complex formed by freshwater refractory organic matter in the presence of trace amounts of Mo(VI). Organic matter is first concentrated by reverse osmosis, then fractionated according to its polarity by the sequential application of DAX-8 and XAD-4 resins. The results obtained show that the voltammetric method measures the refractory organic matter present in the different sewage-derived fractions and that the response obtained follows the trend expected for the fractionation method used (i.e. more hydrophobic fractions largely give the strongest signals). These results have been compared with those obtained from IHSS substances. The results of this study are of particular significance in that it shows that, when applied to surface waters, the voltammetric method measures any refractory organic matter present, irrespective of its origin.

Hydrophobicity and molecular weight of humic substances on ultrafiltration fouling and resistance

Humic substances are the major foulant during ultrafiltration (UF) of wastewater. This study evaluates the effects of hydrophobicity and fractionated humic substances on UF fouling and permeation resistance. A commercial humic acid (HA) obtained from Aldrich was subjected to DAX-8 resin for fractionation of hydrophobic and hydrophilic fractions. These fractions were fractionated further into different molecular weight groups using gel filtration chromatography. The hydrophilic fraction exhibited the greatest flux decline, revealing that hydrophobicity decreases fouling. Since the size of particle fractions was significantly smaller than the pore size of membranes, fouling was greatest for the largest fraction with a 100-kDa membrane and the smallest fraction with a 10-kDa membrane. Severe fouling was due to adsorption and pore blocking. For the first 300 min of filtration, the fouling rate was high in all fractions and is more for 100-kDa than 10-kDa membrane due to greater hydraulic resistance of the HA deposit on the membrane surface. The effect of resistances was also investigated. Each operationally defined resistance depended on membrane pore size, pressure, and HA characteristics. For hydrophobicity and the molecular weight effect, the hydrophilic fraction has the strongest resistance. This study suggested that strong resistance is responsible for irreversible fouling and that is primarily due to pore adsorption and pore blocking.

Effects of the maturity of wood waste compost on the structural features of humic acids

An analytical scheme for the separation of humic substances (HSs) and non-humic substances (non-HSs) was established to estimate the humification index (HI), which was defined as the ratio of HS carbon content to non-HS carbon content. The alkaline compost-extract contained a mixture of HSs and non-HSs, while acidification of the compost-extract resulted in precipitation of humic acid (HA). The acidified supernatant contained fulvic acid (FA) and non-HSs. In the present study, DAX-8 resin was used to separate FA and non-HSs. HI values, which were estimated to evaluate the maturity of wood waste compost, increased with composting duration. To determine the effects of compost maturity on HA structural features, correlations between HI and indicators of the degree of HA humification (atomic ratios, acidic functional group contents, spectroscopic parameters and molecular weight) were investigated. HI values were significantly related to the indicators of the extent of HA humification during composting.

Speciation of Arsenic from Soil Organic Matter in Abandoned Gold and Silver Mines, Korea

Organic forms of arsenic (As) were determined through fractionation procedure of soil organic matter (SOM) in soil, sediments and mine tailing samples from the Myungbong, Dongil, and Okdong mining areas of southern Korea. An alkaline extraction method was applied to soil samples followed by the fractionation procedures of SOM by the DAX-8 and XAD-4 resin adsorption method. Major fraction of organic As species (42% to 98%) was found in acid-soluble fraction, whereas minor fraction (0.1 % to 67.8%) was present in the humic-associated As. In acid-soluble fractions, the transphillic- and hydrophilic-associated As were dominant in addition to As binding with humic and fulvic SOM. Arsenic binding was the strongest between pH 6 to 8 and reduced to about 70% at both low and high pH regions. The amount of both transphillic and hydrophillic associated As was less changed than humic and fulvic-associated As, in both low and high pH regions. This apparently indicates that As has stronger affinity towards hydrophillic rather than hydrophobic organics. From the experimental observation of As-binding SOM in natural soil, the ligand exchange model may be a feasible explanation of transphillic and hydrophillic affinity of As.

The effects of natural organic matter (NOM) fractions on fouling characteristics and flux recovery of ultrafiltration membranes

Natural organic matter (NOM) which is a complex mix of particulate and soluble materials in surface water has been identified and reported by previous studies as responsible for membrane fouling. However the component of NOM which primarily causes the fouling problem is still not well understood, especially relating to the specific fraction that is mainly responsible for flux decline. Therefore, the main objective of this study is to gain a better understanding on the ultrafiltration membrane fouling characteristics due to fractionated NOMs. The 68 kDa MWCO polysulfone (PSF) and 50 kDa MWCO cellulose acetate (CA) membranes formed by a simple phase inversion technique were employed, and the experiments were carried out in a submerged membrane configuration. The Ulu Pontian River water was fractionated into several components which were hydrophobic (HPO), transphilic (TPI) and hydrophilic (HPI) fractions using DAX-8 and XAD-4 ion exchange resins. The experimental results showed that the HPI component of NOM exhibited the worst flux decline despite lesser DOC and UV 254 rejections compared to other fractions (HPO and TPI). On the other hand, the HPO fraction showed the highest DOC and UV 254 removals despite possessing lower organics concentration than HPI fraction. Therefore the degree of flux decline is not necessarily proportional with the DOC and UV 254 removals and in fact the degree of DOC and UV 254 rejections are relatively independent of the amount of organics in the source water. Thus, it is worth to note that rejection and fouling are not greatly dependent on the SUVA and DOC concentrations but mostly on the rejection mechanism resulted from the membrane-feed interactions. The hydraulic resistance in series assessment elucidated that the concentration polarization, adsorptive fouling and cake layer deposition were the dominant fouling mechanisms for HPO, HPI and TPI fractions, respectively. Furthermore the effect of cleaning solutions on flux recovery was found significant in nearly restoring the initial membrane permeability. Surprisingly, the HPI fraction was found to exhibit better flux recovery than HPO fraction despite its higher adsorption resistance ( R a ). Therefore, in future applications, the type of fouling resistance and the dominant fouling mechanism are useful tools which can be employed as quantitative measurements for flux recovery and cleaning techniques effectiveness.

Characterization of dissolved organic matter in leachate discharged from final disposal sites which contained municipal solid waste incineration residues

The properties of dissolved organic matter (DOM) in the leachates discharged from lysimeters and landfill sites containing municipal solid waste incineration residues (MSWIRs) were studied. DOM samples were divided into hydrophobic acid, base, neutral (Hpo-A, Hpo-B, Hpo-N) and hydrophilic (Hpi) fractions using the fractionation method employing DAX-8 resin. Hpi was the smallest fraction of all the raw leachate samples. The proportion of Hpo-N increased with increasing operating time. Landfill sites containing abundant non-combustible wastes showed a higher proportion of Hpo-B than Hpo-A. The molecular weights and functional groups of the DOM fractions were studied by using gel permeation chromatography and FTIR, respectively. In addition, the fluorescent properties and binding sites of the DOM fractions were investigated using fluorescence analysis. In the synchronous scan spectra of each DOM fraction, most of DOM fractions showed an emission peak for the main fluorophores at around 300 nm or 350 nm, which are regarded as aromatic amino acid-like fluorophores. The interaction between the DOM fraction and the pollutants (Cu 2+, pyrene and phenanthrene) was investigated using the fluorescence quenching method. It was observed that the aromatic amino acid-like fluorophores in the DOM fractions could be an important factor affecting complexation with the pollutants.

Isolation and seasonal effects on characteristics of fulvic acid isolated from an Australian floodplain river and billabong

Fulvic acids from an Australian floodplain river and billabong were isolated using DEAE and DAX-8 resins, and characterised with the use of size exclusion chromatography and solid-state CP-MAS (13)C NMR spectroscopy. Differences between the two resin isolates were evident. Fulvic acids isolated using DEAE-cellulose had higher apparent M(n) and M(w) values, while the DAX-8 resin showed a slight preference for aliphatic components. Fulvic acids from the river and billabong had the same functional groups present, however, the river fulvic acids had higher apparent M(n) (number average molecular weight) and M(w) values (weight average molecular weight), and were more polydisperse than the billabong fulvic acid. There were no significant changes in the characteristics of the fulvic acid isolated from the river at four sampling times: summer, autumn, winter and spring. In contrast, fulvic acids isolated from a billabong displayed seasonal variation in molecular weights. This work emphasizes the importance in ecological studies of isolation procedure for the operationally defined fulvic acids.

Comparison of DAX-8 and XAD-8 resins for isolating disinfection byproduct precursors

XAD fractionation has been widely used for isolating natural organic carbon into different fractions for disinfection by-product (DBP) formation tests. The widely used Amberlite ® XAD-8 resin is no longer commercially available and Supelite™ DAX-8 resin has been substituted in recent research. The objective of this study was to evaluate the differences, in terms of reactivity in DBP formation, among the dissolved organic carbon (DOC) fractions isolated by these two resins. DOC collected from two rivers and two soils in the Sacramento–San Joaquin Watershed was fractionated in parallel by the non-ionic macroporous DAX-8 and XAD-8 resins into hydrophobic and hydrophilic fractions. Four parameters used to predict DBP formation in the water industry were evaluated: specific ultraviolet absorbance at 254 nm (SUVA 254 ), differential ultraviolet absorbance at 272 nm (ΔUVA 272 ), specific trihalomethane formation (STHMFP) and specific haloacetic acid formation (SHAAFP). Results indicated that the sorption efficiency of DAX-8 resin was systematically greater than that of XAD-8 resin in our testing conditions and separated an average of 4% more humic substances. Hydrophobic and hydrophilic fractions isolated by XAD-8 and DAX-8 resins showed no significant difference in DBP reactivity ( p >0.05), except for the hydrophilic fraction of the peat soil extracts. Our results indicated their comparability in general use for isolating DBP precursors from bulk aquatic humic substances. However, the fractions of soil humic substances, particularly organic-rich soil, isolated by these two resins may have different chemical characteristics.

Separation of Fulvic Acid from Soil Extracts Based on Ion-Pair Formation with a Cationic Surfactant

A novel method for separating fulvic acid (FA) from soil extracts is proposed. The FA, defined as the acid-soluble fraction of an alkaline extract of soil, was separated based on the precipitation of an ion-pair with a cationic surfactant, such as domiphen bromide. The precipitate was dissolved in aqueous HCl to produce H+ -type FA and a surfactant chloride (SUR-Cl). SUR-Cl, in the aqueous solution, was removed by extraction with CHCl3. After the aqueous phase was passed through a cation-exchanger (H+ -type), H+ -type FA (FA-SUR) was obtained as a powder by lyophylization. The chemical characteristics of FA-SUR were compared with an FA sample separated according to the method of the International Humic Substances Society using a DAX-8 resin (FA-DAX). The oxygen content, O/C atomic ratio and total acidity of the FA-SUR were significantly larger than the corresponding values for FA-DAX. The solid-state CPMS 13C NMR spectra indicated that the higher oxygen content of the FA-SUR could be due to alcoholic hydroxyl groups and polysaccharides as well as carboxylic groups. These results show that FA-SUR is more polar and hydrophilic than FA-DAX.

Characterization of haloacetic acid precursors in source water

Raw water from the Bangkok (Thailand) main municipal water supply canal was examined for its natural organic composition by fractionation with adsorption resins. DAX-8 resin was the first resin employed to fractionate the hydrophobic fractions. Fractionation at neutral pH resulted in the separation of the hydrophobic neutral components; at a high pH level (approx. 10) separation of the hydrophobic base components occurred; and at a low pH level (approx. 2) the hydrophobic acid components were separated. AG-MP-50 cationic resin was then used to separate the hydrophilic base components, and WA-10, a weak anionic resin, was applied finally to fractionate the hydrophilic acid and neutral components. Subsequently, each fraction was tested for its chlorine disinfection by-product (DBP) formation potential. The HAA formation tests demonstrated that the various organic fractions had different reactivity levels for the formation of haloacetic acids (HAAs). For this source water, the hydrophilic neutral fraction dominated over the other five fractions in being the main organic component and the most significant precursor of HAAs formation. On the other hand, in terms of specific HAA formation potential (FP), the hydrophobic and hydrophilic base fractions were the most reactive precursors to the formation of HAAs. In all cases, the quantity of HAAs formed depended linearly upon the amount of organic constituents in the water sample.

Sorption of aquatic humic matter by DAX-8 and XAD-8 resins: Comparative study using pyrolysis gas chromatography

Aquatic humic solutes were separated in parallel by the non-ionic macroporous DAX-8 and XAD-8 resins from four different fresh water sources. The sorptive power of the DAX-8 resin was systematically somewhat greater compared to that of the XAD-8 resin. The DAX-8 resin seems to have more precise column characteristics compared with the XAD-8 resin. According to the tetramethylammonium hydroxide (TMAH) procedure followed up with pyrolysis gas chromatography–mass spectrometry (Py-GC–MS) the content and quality of aliphatic carbons were the most systematic and powerful discriminating factors between the humic extracts obtained by these two resins. Generally speaking, the DAX-8 and XAD-8 resins seem to isolate humic solute bulks almost equally, although the content of aliphatics is slightly greater for the former, producing mixtures with similar structural compositions for general purposes. The environmental impact was also visible on the quality of the structural fine chemistry of the different humic isolates obtained both by the DAX-8 and XAD-8 resins.

Characterization, differentiation and classification of aquatic humic matter separated with different sorbents: synchronous scanning fluorescence spectroscopy

Aquatic humic solutes were separated by the non-ionic macroporous XAD-8 and DAX-8 resins and a weakly basic DEAE cellulose anion exchanger from seven different fresh water sources. Synchronous fluorescence spectroscopy was applied for characterization, differentiation and classification of the different humic-solute aggregates. Fluorescence properties verified that humic-solute fractions isolated parallelly with the non-ionic XAD-8 and DAX-8 resins resembled very closely each other speaking strongly for their structural similarities. DAX-8 resin separated ca. 19% more aquatic humic matter than did the analogous XAD-8 resin. It was possible to tentatively differentiate the untreated water samples according to their fluorescent materials. Several distinct classes of chromophores were detected in both DOM and isolated humic fractions by the synchronous technique: λ ex/ λ em 280/298, 330/348, 355/373, 400/418, 427/445, 460/478, 492/510 and 516/534 nm.

Comparisons of sorption of aquatic humic matter by DAX-8 and XAD-8 resins from solid-state 13C NMR spectroscopy's point of view

Aquatic humic solutes were separated in parallel by the non-ionic macroporous DAX-8 and XAD-8 resins from four different fresh water sources. On average, the sorptive power of the DAX-8 resin does not differ systematically from that of the XAD-8 resin. The DAX-8 resin seems to have more precise column characteristics compared with the XAD-8 resin. There was no significant difference between the major elemental compositions of the parallel humic-solute bulks obtained by these two resins. According to the 13C NMR spectroscopy the content and quality of aliphatic carbons, especially those representing terminal methyl groups or methylene carbons, were the most systematic and powerful discriminating factors between the humic extracts obtained by these two resins. Generally speaking the DAX-8 and XAD-8 resins seem to isolate humic-solute bulks almost equally, although the content of aliphatics is slightly greater for the former, producing mixtures with similar structural compositions for general purposes. The structural composition and quantity of the humic-solute mixture isolable with a weakly basic DEAE-cellulose anion exchange resin differs partially from any humic fraction obtained by non-ionic sorbing solids. The environmental impact was also visible on the quality of the structural fine-chemistry of the different humic isolates obtained both by the DAX-8 and XAD-8 resins.